The present invention relates to lubricating oil compositions and concentrates therefor containing metal core compounds, specifically polynuclear molybdenum core compounds.
Certain oil-soluble or oil-dispersible metal core compounds, ie compounds having a metal core bonded to one or more ligands, are known as additives (or additive components) for lubricating oil compositions (or lubricants) for improving the composition""s properties and performance. The ligand or ligands confer oil-solubility on the compound. For example, certain oil-soluble molybdenum- and sulfur-containing compounds have been proposed and investigated as lubricant additives. U.S. Pat. Nos. 2,951,040; 3,419,589; 3,840,463; 4,966,719; 4,995,996; and 4,978,464 are representative of patent specifications describing molybdenum- and sulfur- containing compounds.
Molybdenum compounds for use as lubricant additives described in the art are principally dinuclear molybdenum compounds, characterised by the oxidation state Mo(V). See, for example, U.S. Pat. No. 5,627,146. Also, EP-A-0 960 178, based on International Patent Application No. PCT IB97/01656, describes use of trinuclear molybdenum compounds as lubricant additives, i.e. characterised by a different oxidation state (Mo(IV)).
Such dinuclear molybdenum compounds may be exemplified by the formula Mo2OxSyL2, and such trinuclear molybdenum compounds may be exemplified by the formula MO3SkL4, where x+y=4, k is at least 4, and L represents a monoanionic ligand for conferring oil-solubility or oil-dispersability on the compound, a typical example being a dithiocarbamate, frequently referred to as xe2x80x9cdtcxe2x80x9d.
The above-exemplified compounds have Mo: ligand (L) molar ratios of 1:1 and 3:4 respectively, ie the number of moles of Mo never exceeds the number of moles of ligand L. Since the Mo is an active part of the compound, it would be desirable to increase its proportion, relative to ligand L, in order to reduce the raw material cost of making the compounds. The art does not describe any such accomplishment, even though it would be beneficial to do so.
The present invention solves the above problem and provides oil-soluble or -dispersible compounds with polynuclear Mo cores whose Mo content exceeds its solubility or dispersibility conferring ligand content.
In a first aspect, the invention is a lubricating oil composition comprising, or made by mixing, a major amount of an oil of lubricating viscosity and a minor amount of, as an additive, at least one compound comprising a polynuclear, such as a di- or trinuclear, molybdenum core and bonded thereto one or more monoanionic ligands capable of rendering the compound oil-soluble or oil-dispersible, wherein the ratio of the number of molybdenum atoms in the core to the number of said ligands is greater than 1:1, such as 3:2 or greater. The compound may provide at least 1, for example 1 to 2000, such as 5 to 1000, preferably 20 to 1000, ppm by mass of the Mo, expressed as Mo atoms, based on the mass of the composition.
Preferably, the molybdenum core, as a Mo cluster core comprising more than one Mo atom, is dinuclear or trinuclear. It may contain non-metallic atoms consisting wholly or partly of sulphur. Preferably it consists of trinuclear molybdenum and sulphur. The ligands or ligands may, for example, be bidentate ligands, e.g. bonding to the core through two sulphur atoms.
The lubricating oil composition according to the first aspect of the invention has excellent antiwear, antioxidant, and friction-reducing properties; also it may be compatible with other additives used in formulating commercial lubricating oil compositions and can be made from readily available starting materials.
In a second aspect, the invention is an additive concentrate for blending with an oil of lubricating viscosity comprising, or made by mixing, an oleaginous carrier and from 1 to 200,000, for example 50 to 150,00, such as 50 to 100,000, ppm by mass of the Mo, expressed as Mo atoms, of an additive defined in the first aspect of the invention, based on the mass of the concentrate.
In a third aspect, the invention is a method of lubricating an internal combustion engine comprising operating the engine and lubricating the engine with a lubricating oil composition of the first aspect of the invention.
In a fourth aspect, the invention is use of an additive as defined in the first aspect of the invention for enhancing one or more lubricating oil properties of a lubricating oil composition.
In a fifth aspect, the invention is a method of making a lubricating oil composition or an additive concentrate comprising mixing an additive defined in the first aspect of the invention with an oil of lubricating viscosity or an oleaginous carrier.
In this specification:
xe2x80x9ccomprisingxe2x80x9d or any cognate word is taken to specify the presence of stated features, integers, steps or components, but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof;
xe2x80x9cmajor amountxe2x80x9d means in excess of 50 mass % of the composition;
xe2x80x9cminor amountxe2x80x9d means less than 50 mass % of the composition, both in respect of the stated additive and in respect of the total mass % of all of the additives present in the composition, reckoned as active ingredient of the additive or additives;
the invention also provides the product obtained or obtainable as a result of any reaction between the various additive components of the composition or concentrates, essential as well as customary and optimal, under the conditions of formulation, storage or use;
xe2x80x9coil-solublexe2x80x9d or xe2x80x9cdispersiblexe2x80x9d used herein do not necessarily indicate that the compounds or additives are soluble, dissolvable, miscible, or capable of being suspended in the oil in all proportions. These do mean, however, that they are, for instance, soluble or stably dispersible in oil to an extent sufficient to exert their intended effect in the environment in which the oil is employed. Moreover, the additional incorporation of other additives may also permit incorporation of higher levels of a particular additive, if desired.